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Comment by dmitri1981 | Hacker News Reader

dmitri1981

Here is an excellent rebuttal of the whole concept: http://www.monbiot.com/archives/2010/08/16/towering-lunacy/

In summation, the bottleneck is light, or, basically, energy.

This is one of the reasons it's so important for us to press on with technology and not just try to keep things the same; we need better, more cost-effective energy, such as with better nuclear power plants. If we have that, there's a lot of things like this that open up to us that can allow us to save energy in other ways. If we don't progress, though, we'll be stuck with a resource-expensive society and no way to escape from the trap.

That's not really a fair summation, if you ask me. Yes, light is the immediate bottleneck, but as Monbiot says, it requires "all the usual rules of business, economics, physics, chemistry and biology to be suspended to make way for his idea."

Even with more cost-effective energy, this is still a terrible idea.

Monbiot makes the common mistake of starting with Manhattan real estate for his rebuttal, which I think is naive enough to be considered a strawman argument.

As for lighting, the trick is to figure out how to use natural lighting for a majority of the input. Obviously, again, this is why 100-story skyscrapers aren't practical, but sub-10 story warehouses could be. Although some are investigating architectural ideas like mirrors and other hacks.

"the trick is to figure out how to use natural lighting for a majority of the input."

No, that really is impossible. Mother Nature's little growers are optimized for the amount of sunlight they receive on flat ground, and by trying to stack farms on top of each other you utterly inevitably mathematically reduce the amount of sunlight each floor can get to substantially less than that, because the floors occlude each other, except the top floor. To the extent that people fail to take that into account they really are failing at physics badly and Monbiot is correct to criticize them.

I think under the right circumstances and with plausible technological development this can make sense, but he's absolutely correct that doing it with current technology is completely infeasible and useless. My position is actually not what he is criticizing, and I'm still open to the possibility that while the future may look different, the actual best solution is something not yet evident. We may also simply reduce the costs of transportation such that growing something 1000 miles away simply isn't that big a deal ecologically. (We really, really, really need cheap energy, cheap in all senses of the term, ecologically as well as economically. And there are feasible possibilities.)

I don't think Manhattan real estate is a strawman-- the point is, in order for this concept to work, you would need to be able to buy a city block in whatever metropolitan area for cheaper than you could buy enough land in the outskirts to grow an equivalent quantity, plus the transportation costs.

And sub-10-story warehouses only magnifies the problem-- then you need to buy even more city blocks.

A city block in many metros is not that much money though. Think Cleveland.

The problem this is seeking to fix is to localize food production as best as possible. And that's in the context of the current situation, where food is not produced in the outskirts, but halfway across the world.

Purchasing land 30 miles outside of a city falls well within the confines of urban agriculture, especially since indoor ag means a year-long growing cycle. This means that Detroit or Iceland don't need to rely on South American growers for certain seasonal items.

The small shipping distance necessary for putting these in New Jersey, greater Chicagoland, etc., there's no argument against that, but yet, people keep citing downtown Manhattan as impractical for farming. Of course it's impractical for farming, it's damn near impractical for living.

If you want to use natural lighting, you're going to need to increase the light catchment area beyond the area of the building. One layer of crops already wants a full dose of sunlight, so splitting the amount of solar energy which hits a single building between 10 floors will just leave each floor with 10% of what it actually needs. About the only way I can think it could possibly work is if the roofs of all the buildings around the vertical farm were fitted with sun-tracking mirrors, but that assumes both that the roofs are available and not used for, say, solar electricity generation, and that you don't want to put vertical farms too close together.

> One layer of crops already wants a full dose of sunlight

Is that actually true? Crops are grown in a pretty wide range of locations, and sometimes the same crops are grown in different locations with quite different insolation. Surely there must be at least some set of [location,crop] pairs where the crop needs less than the full amount of sunlight available in that location?

Sure, but you'd then be limiting the applicability of the idea quite a lot, which goes very much against the idea that this can be used to chop delivery distances down.

I also find it hard to believe that you could find 10 layers' worth of crops this would work with. Two or three, maybe, but I would be astonished by more than that.

> we need better, more cost-effective energy, such as with better nuclear power plants

I don't think this will work. Some numbers:

* USDA says 70 bushels/acre of wheat is the average yield for irrigated fields [1]

* perhaps a theoretical 3 harvests/year [2] could be possible in a climate-controlled building (it takes 110-130 days between planting and harvest), for 210 bushels/acre/year

* solar irradiation amounts to an annual average of about 4 kWh/day/m^2 = 170 W/m^2 in the wheat belt [3], or up to about 6.5 kWh/day/m^2 = 270 W/m^2 average in July

* March 2011 wheat futures are $7.67/bushel on the CME [4]

So I reason: with the cheapest $0.05/kWh electricity (nuclear, hydro, or coal at large-buyer rates), the cost to imitate sunlight, with "100% efficient" lighting (maybe LEDs), would be in the range of $300,000-$500,000/acre per year [5]. (I think the higher figure is closer -- it corresponds to sustaining July-level insolation year round, which would make sense for year-round planting). Which divides up to about $2,500/bushel -- over 300 times current prices. (For household-scale perspective, this is $70/liter).

You can get incremental improvements in power plant economics, but not orders of magnitude (not anytime soon). Given current technology and economics, this idea falls apart.

[1] http://ww.agcensus.usda.gov/Publications/2002/Volume_1,_Chap...

[2] http://en.wikipedia.org/wiki/Wheat#Agronomy

[3] http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/ (use "horizontal flat plate")

[4] http://www.cmegroup.com/trading/agricultural/

[5] calculation: http://www.google.com/#sclient=psy&hl=en&q=0.05+USD%...

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